Device and method for applying a flowable medium onto a moving surface

ABSTRACT

An apparatus for the application of a flowable medium ( 2, 2 ′) from a stock chamber ( 7, 8 ) to a surface ( 6 ) being moved along the apparatus, and to the use of an apparatus of this type. The stock chamber ( 7, 8 ) partly covers the surface ( 6 ), with formation of a sealing gap ( 14 ) and an exit gap ( 18 ). In order to prevent the formation of air bubbles in the medium ( 2, 2 ′), it is proposed to divide the stock chamber ( 7, 8 ) into a pre-chamber ( 7 ) and a main chamber ( 8 ). A dividing element ( 10 ) which, together with the surface ( 6 ), limits a dividing gap ( 15 ), is arranged between the chambers. Various shapes of the dividing element are proposed. The apparatus is particularly suitable for the application of a polymer dispersion to the surface ( 6 ). A process for operating an apparatus of this type is also described.

The invention relates to an apparatus and a process for the applicationof a flowable medium from a stock chamber to a surface moved along theapparatus, where the stock chamber partly covers the surface withformation of a sealing gap and an exit gap. The invention furthermorerelates to the use of an apparatus of said type.

Apparatuses of said type are widely employed, for example, in theproduction of labels for coating paper or film webs with adhesives. Acommon process for this purpose is the engraved roll applicationprocess, in which the flowable adhesive is located in an open stockchamber whose opening is in contact with a rotating roll. The rollcontains a multiplicity of engraved grooves. During rotation of theroll, the initially empty grooves enter the opening region of the stockchamber from the outside and are filled with adhesive therein. On exitof the roll from the opening region of the stock chamber, excessadhesive is wiped off the surface of the roll by means of a doctor bladewhich extends over the width of the roll and limits the opening regionof the stock chamber. During further rotation of the roll, the latter isbrought into contact with the paper or film web to be coated, causing atleast some of the adhesive in and on the grooves to be transferred tothe web.

The amount of adhesive transferred from the stock chamber to the rollcan be varied within narrow limits through the position or contactpressure of the doctor blade at the exit of the roll from the openingregion of the stock chamber, i.e. ultimately through the height of theexit gap formed by the doctor blade and the roll surface.

A further doctor blade is generally installed in the region of the entryof the roll into the opening region of the stock container, this furtherdoctor blade taking on the function of a seal between the stockcontainer and the roll surface. In order to prevent excess outflow ofthe adhesive at this point, the sealing gap formed between this doctorblade and the roll surface must have the smallest possible height.

The contact pressure of the doctor blade at the sealing gap and theheight of the exit gap can be adjusted in this known process by changingthe position and situation of the application apparatus relative to therotating roll.

In particular at high roll rotation speeds, complete filling of the rollgrooves is no longer guaranteed in this known process, which results inthe amount of adhesive taken up during a rotation and thus ultimatelythe application weight of the adhesive to the web to be coated droppingin an undesired manner. Furthermore, air is increasingly introduced intothe stock container through the roll grooves at higher rotation speeds,resulting in undesired foaming in the stock container. The presence offoam in the stock container in turn means that the grooves of theengraved roll are not completely filled with adhesive, but insteadpartly with air in the form of bubbles, which means that fine bubblesform on the web to be coated, resulting in undesired clouding of theadhesive layer.

In order to prevent said difficulties, it has been proposed topressurize the adhesive in the stock chamber using suitable means (J.Türk, H. Fietzek, H. Hesser and I. Voges, Perspektiven für dieVerarbeitung von Dispersionshaftklebstoffen, reprint TI/ED 1654d, BASFLudwigshafen, August 1993). This ensures complete filling of theengraved grooves, even at high roll rotation speeds. Depending on theset pressure, a different amount of adhesive is also conveyed out of theapplication apparatus on the surface of the roll outside the engravedgrooves at the exit gap. In this way, the amount of adhesive applied tothe roll and thus ultimately the application weight of the adhesive onthe web to be coated can be set within a broader range than without theuse of pressure. Due to the higher pressure in the stock chamber, it isfurthermore achieved that only a greatly reduced amount of air isintroduced into the stock container at the sealing gap; in this way,excess foaming is prevented.

However, the higher the roll rotation speed, the higher the pressure inthe stock chamber has to be selected in order to prevent theintroduction of air into the adhesive. The maximum achievable rotationspeed is limited by the fact that, on a further increase in pressure,the adhesive is forced out of the stock container in an uncontrolledmanner firstly through the sealing gap and secondly through the exitgap. Exit of adhesive through the sealing gap results in undesiredpresentation of adhesive in front of this gap, which can result insoiling of the environment of the application apparatus and inoperational interruptions. Uncontrolled exit of adhesive through theexit gap in turn results in uneven application of composition to the webto be coated.

In the article “Rasterwalzenauftragsverfahren mit Druckkammerrakel—einBeschichtungswerkzeug auch für strahlenchemisch härtende Systeme”, IPW1/97, pp. 1 to 8, it was proposed to construct an application apparatusin such a way that the adhesive flows constantly through the stockchamber in the opposite direction to the direction of movement of theroll. In this way, air introduced into the stock container is constantlytransported away by the rotating roll with the flowing adhesive. It wasalso proposed in this article to incorporate a throttle element into thestock chamber in such a way that a narrow throttle gap with a length ofa few centimeters forms between the throttle element and the rollsurface, through which gap the adhesive flows in the opposite directionto the direction of movement of the roll surface. In this way, theengravings are filled better with adhesive, and any air present in theengraved grooves is forced out of them, at least partly, and removedfrom the roll surface with the flowing-off adhesive. In practice,however, precise adjustment of the throttle element independently of theoperating parameters, for example roll rotation speed, viscosity andpressure of the adhesive, proves to be difficult and not easilyreproducible. In addition, an apparatus of this type cannot reliablyprevent the introduction of air into the stock chamber and the formationof bubbles in the adhesive film.

It is an object of the present invention to provide an apparatus for theapplication of a flowable medium to a surface moved along the apparatuswhich works reliably even at high surface speeds, in which formation ofair bubbles in the medium is reliably prevented, which is of simpleconstruction, and which can be set simply and reproducibly for givenoperating conditions.

We have found that this object is achieved by an apparatus for theapplication of a flowable medium from a stock chamber to a surface beingmoved along the apparatus, where the application chamber at least partlycovers the surface. In accordance with the invention, the stock chamberis divided into a pre-chamber and a main chamber, between which isarranged a dividing element which, together with the surface, limits adividing gap.

The dividing element arranged between the pre-chamber and the mainchamber reliably prevents air which has entered the pre-chamber frombeing transported into the main chamber and resulting in undesiredfoaming therein. The actual coating of the surface with the desiredamount of the flowable medium then takes place free from air bubbles inthe main chamber. The pre-chamber and the main chamber advantageouslyhave independent feeds for the medium, so that, for example, thepressure conditions in the pre-chamber and in the main chamber can beselected independently of one another.

Particular advantages arise if the dividing element is arranged in sucha way that it touches the surface. This achieves complete separation ofthe pre-chamber and the main chamber.

In practice, complete touching or contact of the dividing element withthe surface can often only be achieved if the surface is stationary. Inactual operation, i.e. in the case of a moving surface, unavoidablevariations in the guidance of the surface mean that a certain, albeitvery small gap height will usually be present. Particularly effectiveprevention of air bubbles and uniform application of the medium to thesurface is also achieved if the dividing element is arranged in such away that the height of the dividing gap between the dividing element andthe surface is between 0 and 0.1 mm, in particular between 0 and 0.08mm, preferably between 0 and 0.05 mm, particularly preferably between 0and 0.02 mm. A minimization of the height of the dividing gap in thisway likewise achieves effective separation of the pre-chamber and themain chamber.

In order to ensure reliable function of the apparatus under variousoperating conditions, it is advantageous for the dividing element to bearranged in a movable manner. Movement can consist both in a change inthe situation of the dividing element, for example a tilting, a movementin or against the direction of movement of the surface or a movementtoward or away from the surface, i.e. a change in the height of thedividing gap. Operating conditions which influence the optimum positionand situation of the dividing element can be, for example, the natureand speed of movement of the surface, the pressure of the medium in thepre-chamber, the pressure of the medium in the main chamber, and thecomposition and viscosity of the medium to be applied.

Simple implementation of the separation of the pre-chamber and the mainchamber arises if the dividing element contains a doctor blade. However,other embodiments of the dividing element are also conceivable.Particularly effective separation can be achieved if the dividingelement is a double doctor blade. An essential prerequisite for thechoice of a suitable dividing element is its sealing function separatingthe pre-chamber from the main chamber.

In an advantageous embodiment, the dividing element contains acylindrical rod. This facilitates reliable and low-wear sealing betweenthe pre-chamber and the main chamber.

Effective sealing can also be achieved if the dividing element containsa flexible leaf which is arranged in such a way that at least one edgeof the leaf touches the surface in a resilient manner.

Particularly effective sealing between the pre-chamber and the mainchamber can advantageously be achieved by designing and arranging thedividing element in such a way that it, together with the movingsurface, limits at least two dividing gaps, where the height of eachdividing gap is between 0 and 0.1 mm, in particular between 0 and 0.08mm, preferably between 0 and 0.05 mm, particularly preferably between 0and 0.02 mm. In a particularly preferred embodiment, the dividingelement is arranged in such a way that the height of each dividing gapis 0 mm, i.e. the dividing element touches the moving surface.

The division of the stock chamber into a pre-chamber and a main chamberenables individual operating parameters to be modified separately forthe pre-chamber and for the main chamber. In an advantageous embodimentof the invention, means are present with which the pressure of themedium in the main chamber can be set independently of the pressure ofthe medium in the pre-chamber. For example, the pressure in the mainchamber can then be chosen to be higher than the pressure in thepre-chamber. This firstly avoids the medium being forced out of thepre-chamber in an uncontrolled manner through the sealing gap whichseals off the pre-chamber from the outside, and secondly the increasedpressure in the main chamber forces any air bubbles which pass throughthe dividing gap back into the pre-chamber.

Inverse pressure conditions in the pre-chamber and in the main chambercan offer particular advantages. In an advantageous process foroperating the apparatus according to the invention, the pressure of themedium in the pre-chamber is higher than the pressure of the medium inthe main chamber. In this way, penetration of air into the pre-chamberthrough the sealing gap can be effectively prevented from the outset.The pressure in the main chamber can then be varied within broad limitswithout the risk of foaming, in order to guarantee optimum layerapplication to the surface.

Further advantages arise if a throttle gap is additionally arrangedbetween the pre-chamber and the main chamber. The throttle gap can belocated between the pre-chamber and the dividing element or between thedividing element and the main chamber. The height of the throttle gap isalways larger than that of the dividing gap. A throttle gap of this typecan, for example, be formed by a region of the wall between thepre-chamber and the main chamber which is designed in such a way that itruns parallel to the moving surface at a small distance therefrom. It isfurthermore conceivable for a special throttle element to be installedon the wall between the pre-chamber and the main chamber. The dividingelement limiting the dividing gap can in this case be attached to thethrottle element. The throttle element can be arranged so as to beadjustable in position and/or situation. In this way, the height andshape of the throttle gap can be changed. The length of the throttle gapcan vary within broad limits. In particular, a conceivable throttle gapis one whose length is a multiple of the length of the dividing gap. Thethrottle gap can be directly adjacent to the dividing gap, but can alsobe arranged spatially separated therefrom. An important action of thethrottle gap is to reduce the pressure difference between thepre-chamber and the main chamber. In this case, the throttle gap fulfilsa sealing function supporting the function of the dividing gap. If, forexample, the pressure in the main chamber is chosen to be higher thanthe pressure in the pre-chamber, a pressure gradient forms in thethrottle gap, with the pressure dropping from the main chamber to thepre-chamber. Any air bubbles which have penetrated from the pre-chamberinto the throttle gap are in this way additionally held back in thethrottle gap.

Further advantages arise if means are present which allow thetemperature of the medium in the pre-chamber, in the main chamber or inboth chambers to be set independently of the ambient temperature. Thus,for example, the temperature in both chambers can be chosen to besignificantly higher than the ambient temperature. This enables firstlythe viscosity of the medium to be reduced and thus its flow propertiesto be improved, and secondly a drying process following application ofthe medium to the surface is accelerated.

Particular advantages arise if the temperature of the medium in the mainchamber is selected to be higher than that of the medium in thepre-chamber. This reduces the viscosity of the medium in the mainchamber compared with the viscosity of the medium in the pre-chamber,which facilitates penetration of small amounts of the medium from themain chamber into the pre-chamber through the dividing gap, but makestransport of the medium—and thus also of any air bubbles present—fromthe pre-chamber into the main chamber more difficult. Conversely, it isalso conceivable to select the temperature in the pre-chamber higherthan in the main chamber. This reduces the viscosity of the medium inthe pre-chamber, which increases the sealing function of the sealing gapand can effectively prevent penetration of air into the pre-chamber fromthe outside. The temperature in the main chamber can then be selectedindependently of the temperature in the pre-chamber in such a way thatoptimum composition application to the surface is ensured.

Particularly reliable and uniform composition application occurs in thecase where the moving surface has recesses, i.e., for example, is in theform of an engraved roll. The term engraved roll is taken to mean acylindrical roll in which fine grooves have been engraved at regularintervals. However, the recesses can also be punctiform or have anyother geometrical shape desired. The profile of the recesses can alsoadopt any desired forms, for example rectangular or circular.

The apparatus according to the invention is suitable for the applicationof media of a wide variety of types to the surface, for example polymermelts, solutions of polymers in organic solvents or dispersions of awide variety of types. Particular advantages arise on use of theapparatus according to the invention for the application of a polymerdispersion to the surface. In contrast to a homogeneous solution, adispersion is a heterogeneous mixture of a liquid dispersion medium anda dispersed substance finely distributed therein. Of particularpractical importance here are dispersions in which the dispersion mediumis water and the dispersed substance consists of polymer particles. Adispersion of this type is also referred to as an aqueous polymerdispersion. Aqueous polymer dispersions are widely used as adhesives inthe production of labels.

The apparatus according to the invention is particularly suitable forthe application of a contact adhesive dispersion to the surface. Theterm contact adhesive dispersion is taken to mean a dispersion whichcomprises a pressure-sensitive and self-adhesive polymer whose filmformation temperature is below room temperature. The film formationtemperature is the temperature at which the dispersed particles melttogether to form a transparent, crack-free film. A low film formationtemperature can be achieved if a soft polymer, i.e. a polymer having alow glass transition temperature, or a hard polymer to which aplasticizer has been added as additive is used. Polymers based onacrylates and/or methacrylates dispersed in water as dispersion mediumare widely used here.

Preferred embodiments of the invention are explained in greater detailbelow with reference to the drawing, in which

FIG. 1 shows a sketch of the principle of an apparatus according to theinvention for coating a web with a flowable medium,

FIG. 2 shows a diagrammatic sectional side view of an applicationapparatus according to the invention,

FIGS. 3 to 7 show sectional side views of various variants of anapplication apparatus according to the invention, and

FIG. 8 shows a sectional front view of an application apparatusaccording to the invention.

LIST OF REFERENCE NUMERALS

1 web

2,2′ flowable medium

3 application apparatus

4 engraved roll

5 counterroll

6 surface

7 pre-chamber

8 main chamber

9 dividing wall

10 central doctor blade

11 opening of the pre-chamber

12 opening of the main chamber

13 front doctor blade

14 sealing gap

15 dividing gap

16 throttle gap

17 rear doctor blade

18 exit gap

19 engraved groove

20 housing

21 filler piece

22 intermediate plate

23 strip

24 side strip

25 tubular gasket

26 lifting strip

27 plastic leaf

28 clamp strip

29 leaf carrier

30 doctor-blade holder

31 doctor-blade leaf

34 wiper

35 sealing strip

36 spacer strip

37 rod

38 pneumatic connection

39 pneumatic line

40 T-piece

41 lifting cylinder

43 distributor

44 compressed air pipe

45 sealing cap

The apparatus shown diagrammatically in FIG. 1 for coating the web 1with a flowable medium 2, 2′ essentially consists of an applicationapparatus 3, an engraved roll 4 and a counterroll 5. The medium 2, 2′ isapplied to the surface 6 of the rotating engraved roll 4 in theapplication apparatus 3 and is transported to the web 1 by this roll.The web 1 is moved over the surface 6 of the engraved roll 4 by thecounterroll 5 with exertion of pressure, during which the medium 2, 2′is transferred to the web 1 to be coated.

The application apparatus 3 shown diagrammatically in enlarged form inFIG. 2 has a stock chamber which is divided into a pre-chamber 7 and amain chamber 8 by a central doctor blade 10 as dividing element. Themedium to be applied is fed, in each case separately, to the pre-chamber7 and the main chamber 8 through openings 11, 12. The applicationapparatus 3 is covered by the rotating engraved roll 4, the surface 6 ofthe engraved roll 4 moving over the application apparatus 3 in aclockwise direction. A front doctor blade 13 limits the pre-chamber 7 atthe point of entry of the roll surface 6 into the application apparatus3, with formation of a sealing gap 14. The front doctor blade 13 thussatisfies the function of a sealing lip. The central doctor blade 10together with the surface 6 limits a dividing gap 15. Furthermore, thedividing wall 9 together with the surface 6 limits a throttle gap 16,whose height is significantly greater than that of the dividing gap 15and whose length is a multiple of the length of the dividing gap 15.Finally, a rear doctor blade 17 limits the main chamber 8 in the regionof the exit of the roll surface 6 from the application apparatus 3, withformation of an exit gap 18.

In operation, the medium 2, 2′ is pumped through the opening 11 into thepre-chamber 7 and through the opening 12 into the main chamber 8 bymeans of pumps (not shown) . The pressure in the pre-chamber 7 and inthe main chamber 8 is set, in each case separately, by means ofregulation devices, for example reduction valves, which are not shown.In addition, a heating device may be provided in the line to thepre-chamber 7 and in the line to the main chamber 8 in order to set thetemperature in the pre-chamber 7 and in the main chamber 8 separately.

The engraved roll 4 has on its surface 6 a multiplicity of recesses inthe form of engraved grooves 19. The direction of the engraved grooves19 on the surface 6 of the roll 4 has both an axial and a tangentialcomponent, relative to the roll axis. The tangential component here isgenerally significantly smaller than the axial component, i.e. theengraved grooves run helically with a slope which is generally amultiple of the width of the roll. The distance between the grooves onthe surface is typically between 0.2 mm and 0.5 mm, depending on thedesired application weight, and their depth and width are typicallyabout 0.1 mm.

Before entry of the surface 6 into the application apparatus 3, aresidual amount of the medium and a certain amount of air are present inthe engraved grooves 19. The residual amount of the medium is introducedinto the pre-chamber 7 of the application apparatus 3 through thesealing gap 14. The sealing gap 14 is designed in such a way that theamount of air introduced at the same time is kept minimal. This can beachieved, for example, by the front doctor blade 13 being pressedagainst the surface 6 of the engraved roll 4 with exertion of pressure.

A significant improvement in the sealing function arises through thepressure of the medium 2 in the pre-chamber 7 being selected higher thanthe ambient pressure. This causes a certain amount of the medium 2 to betransported constantly to the outside through the sealing gap 14, withthe medium 2 expelling the air present in the engraved grooves 19. Themedium in the sealing gap 14 thus forms a liquid barrier againstingressing air. The medium 2 exiting from the sealing gap 14 iscollected in a trough (not shown in FIG. 2) and fed back into theprocessing circuit.

The excess pressure to be selected in the pre-chamber 7 is preferablyless than 1 bar, in particular in the region of about 500 mbar.Particularly good results have been achieved with an excess pressure inthe range from 300 to 600 mbar. If the pressure in the pre-chamber 7 istoo high, the medium is forced to the outside excessively and in anuncontrolled manner through the sealing gap 14. This may be the caseabove 1000 mbar.

In order to prevent medium which is exiting through the sealing gap orelsewhere dropping onto the surface in an uncontrolled manner, it isadvantageous to arrange the application apparatus 3, as shown in FIG. 1,vertically beneath the engraved roll 4 (“six o'clock position”). It islikewise advantageous to arrange the counterroll 5 vertically above theengraved roll 4 (“12 o'clock position”).

In the pre-chamber 7, the engraved grooves 19 are completely filled withthe medium 2. The engraved grooves 19 filled in this way are transportedpast the dividing gap 15 and the throttle gap 16 into the main chamber 8by the rotation movement of the engraved roll. The central doctor blade10 limiting the dividing gap 15 effectively holds back any air bubblespresent in the pre-chamber 7.

The pressure in the main chamber 8 can be selected independently of thepressure in the pre-chamber 7. Thus, it is possible, in particular, toselect the pressure in the main chamber to be lower than the pressure inthe pre-chamber. Also particularly suitable here is an excess pressureof less than 1 bar compared with the outside. If the pressure in themain chamber 8 is too high, the medium is forced through the exit gap 18to the outside in an uncontrollable manner, which results in unevencoating of the surface 6 of the engraved roll 4 and thus of the web 1 tobe coated. A pressure in the range from 100 to 300 mbar has provensuccessful.

The ratio between the excess pressure in the main chamber 8 and theexcess pressure in the pre-chamber 7 is preferably in the range from 1:2to 1:10, particularly preferably in the range from 1:2 to 1:5. Thehigher pressure in the pre-chamber 7 effectively prevents foaming at thesealing gap 11 from the outset. The application weight can then be setthrough the (lower) pressure in the main chamber 8 independently of thepressure in the pre-chamber 7.

The dividing gap should have the lowest possible height. Completecontact of the central doctor blade 10 with the roll surface 6 ispreferred. However, this frequently cannot be achieved in practice sincethe roll moves and a very small gap height is unavoidable due tovibrations and due to wear. It is appropriate in practice to select theheight of the dividing gap 15 to be less than 0.1 mm, in particular lessthan 0.08 mm. Particularly good results are achieved with gap heights ofless than 0.05 mm.

The surface 6 is coated uniformly with the medium 2′ in the main chamber8 under the pressure prevailing therein. The amount of medium 2′ appliedto the surface 4 is determined, inter alia, by the position of the reardoctor blade 17, which limits the exit gap 18. Depending on theposition, a certain amount of the medium is also applied to the surface6 of the engraved roll 4 between the engraved grooves 19.

In particular for the coating of a web or film with an aqueous polymerdispersion, it has proven successful to use plastic materials, such aspolyethylene, as the material for the central doctor blade 10. Thelength of the dividing gap 15 is preferably less than 5 mm, inparticular less than 2 mm. The length of the throttle gap between thedividing gap and the main chamber is preferably from 2 to 10 cm, inparticular about 5 cm, and its height is preferably greater than 0.2 mm,in particular greater than 0.5 mm.

Specific embodiments of the apparatus according to the invention areshown in FIGS. 3 to 7. In these figures, components which arefunctionally identical are denoted by identical reference numerals, evenif their detailed design is different.

FIG. 3 shows a sectional side view of a particularly preferredapplication apparatus. A filler piece 21 is employed in the housing 20.An intermediate plate 22 on which two strips 23 are mounted is insertedinto the filler piece. Side strips 24 are located on the left and rightof the strips 23. These side strips have recesses in which gaskets 25are located. A lifting strip 26 is run between the side strips 24. Thislifting strip can be moved vertically through pneumatic means with theaid of lifting cylinders 41. In another embodiment, the verticalmovement of the lifting strip 26 can also take place mechanically. Aleaf carrier 29, into which a flexible plastic leaf 27 is inserted, ismounted in the lifting strip. The plastic leaf 27 is bent over and fixedin the leaf carrier 29 by a clamp strip 28. To this end, the clamp strip28 is screwed to the leaf carrier 29.

Two doctor-blade holders 30 are attached to the housing 20 in the leftand right external regions thereof. A doctor-blade leaf 31 is attachedin each case between the filler piece 21 and the doctor-blade holders30.

An engraved roll 4 is located above the application apparatus. Thedoctor-blade leaves 31 are arranged in such a way that they each limit agap together with the engraved roll 4. On rotation of the engraved roll4 in the clockwise direction, the gap between the right-handdoctor-blade leaf 31 and the engraved roll 4 functions as sealing gap,and the gap between the left-hand doctor-blade leaf 31 and the engravedroll 4 functions as exit gap. The plastic leaf 27 clamped between theleaf carrier 29 and the clamp strip 28 functions as dividing element,which divides the space limited by the surface of the engraved roll 4and the two doctor-blade leaves 31 into a pre-chamber 7 and a mainchamber 8.

The position of the plastic leaf relative to the surface of the engravedroll 4 can be adjusted vertically via the lifting strip 26. Thisenables, in particular, the contact pressure acting on the plastic leaf27 to be set. The plastic leaf 27 thus produces effective separationbetween the pre-chamber 7 and the main chamber 8. The separating actionis reinforced by the resilient properties of the plastic leaf 27.

In operation, the pre-chamber 7 and the main chamber 8 are filled withthe medium via drilled holes (not shown). The pressure and temperatureof the medium in the pre-chamber 7 and of the medium in the main chamber8 can be set independently of one another. If medium from thepre-chamber 7 or the main chamber 8 enters the intermediate spacebetween the clamp strip 28 and the engraved roll 4, it can flow out ofthis intermediate space via a drilled hole.

The position of the right-hand doctor-blade leaf 31 is selected in sucha way that a small amount of the medium in the pre-chamber 7 constantlypasses out of this chamber through the sealing gap. This forms a liquidbarrier against ingressing air at the sealing gap. The exiting mediumflows over the right-hand doctor-blade holder 30 into a trough (notshown) . The left-hand doctor-blade leaf is adjusted in such a way that,in combination with the other operating parameters, such as the pressureof the medium in the main chamber 8, its temperature, its viscosity,etc., the desired application thickness is achieved on the engraved roll4.

The plastic leaf 27 is preferably made of a flexible plastic, such aspolyester. Its thickness is preferably about 0.5 mm. By contrast, boththe clamp strip 28 and the leaf carrier 29 preferably consist of asuitable metal alloy, as do the filler piece 21, the intermediate plate22, the strip 23 and the side strips 24. The gasket between the sidestrips 24 and the lifting strip 26 is designed as an inflatable tubulargasket 25. It consists of a tube, preferably of silicone, which isfilled with compressed air and thus achieves its sealing function.

FIG. 4 shows a variant of an application apparatus according to theinvention. Instead of a plastic leaf, a solid wiper 34 serves as sealingelement between the pre-chamber 7 and the main chamber 8 here. The wiperis preferably made of polytetrafluoroethylene (PTFE). A wiper of thistype can also ensure effective sealing between the pre-chamber 7 and themain chamber 8; significant material transfer does not occur between thepre-chamber 7 and the main chamber 8 or vice versa.

A further variant of the application apparatus is shown in FIG. 5. Heretoo, the dividing element between the pre-chamber 7 and the main chamber8 contains a solid wiper 34. A cylindrical rod 37, which, like the wiper34, is preferably made of PTFE, is additionally located in a recess ofthis wiper. Owing to the ability of the rod 37 to rotate, the frictionbetween the engraved roll 34 and the dividing element is reduced. Thisalso reduces wear of the dividing element. At the same time, thepunctiform contact between the surface of the engraved roll 4 and therod 37 ensures that a good sealing action is achieved.

FIG. 6 shows a further variant. In FIG. 6, the doctor-blade holder 30and the doctor-blade leaves 31 are not shown, but are just as necessaryin operation as in FIGS. 3 to 5. The dividing element between thepre-chamber 7 and the main chamber 8 has a multi-part construction here.It consists of two sealing strips 35 which taper to a point at the topand are separated by a spacer strip 36. A cylindrical rod 37 is insertedinto the interspace between the surface of the engraved roll 4 and thespacer strip 36. This design results in very good separation between thepre-chamber 7 and the main chamber 8. Due to their shape tapering to apoint at the top, the sealing strips 35 ensure reliable sealing, whichis further reinforced by the rod 37.

Finally, a further variant of the application apparatus is shown in FIG.7. Here too, two sealing strips 35 which taper to a point at the top arepresent, with a wiper 34 between them. This design enables, as indicatedin FIG. 7, the provision of a run-off for the medium, which, if desired,runs from the pre-chamber 7 or the main chamber 8 into the interspacebetween the sealing strips 35.

FIG. 8 shows a front view of an application apparatus according to theinvention as shown in one of FIGS. 3 to 7. FIG. 8 illustrates, inparticular, the pneumatic connections for vertical movement of thelifting strip 26. For better clarity, the feed to the pre-chamber 7 andthe main chamber 8 is not shown in FIG. 8. The lifting cylinders 41,which are connected to the lifting strip 26, which is not shown in FIG.8, are provided with pneumatic connections 38. These are connected viaT-pieces 40 and a pneumatic line 39. The lifting cylinders can becharged with compressed air in a controlled manner via this line. Thisenables the vertical position of the lifting strip 26 to be setprecisely. A commercially available pneumatic apparatus is used for theprovision of the compressed air for the pneumatic system. In anotherembodiment, the adjustment is instead carried out mechanically.

The pneumatic connection by means of which the tubular gaskets 25 arepressurized is also visible in FIG. 8. The end of a tubular gasket 25projects out of the application apparatus to the right. A distributor43, which is connected to a compressed-air supply 44, is attached tothis end. The tubular gasket is provided with a sealing cap 45 at itsleft-hand end.

The entire apparatus shown in FIG. 8 is located in a trough (not shown)which collects medium exiting and overflowing from the sealing gap andreturns it to the processing circuit.

The apparatuses described are used, in particular, in label manufacturein the coating of paper or film webs with adhesives. The adhesives canbe of various types. For example, use is made of polymer melts which areapplied to the web at elevated temperature and are then cooled.Rubber/resin mixtures and solutions of synthetic polymers are alsowidely used.

Dispersions are particularly important. In these, particles, preferablyof a polymer, are dispersed in a dispersion medium, preferably water.After application of the dispersion to the web to be coated, thedispersion medium is removed in a drying unit, causing the particles tomelt together and form the self-adhesive surface.

The dispersions used in label.manufacture are so-called contact adhesivedispersions, i.e. dispersions in which the film formation temperature ofthe dispersed polymer is below room temperature. The dispersed polymersused are in particular polymers based on (meth)acrylates and, to alesser extent, vinyl ether polymers. Irrespective of the precisecomposition of the monomers, polymers of this type arepressure-sensitive and self-adhesive without additives being admixedwith them. Preference is given here to so-called soft polymers, i.e.polymers having a low glass transition temperature.

Processes for the preparation of such polymers are adequately known tothe person skilled in the art. A common process is so-called emulsionpolymerization, in which polymerizable, olefinically unsaturatedcompounds (so-called monomers) are emulsified in water with the aid ofsurface-active compounds and polymerized with use of water-solubleinitiators.

Of particular industrial importance are so-called main polymers selectedfrom C₁-C₂₀-alkyl (meth)acrylates, vinyl esters of carboxylic acidscontaining up to 20 carbon atoms, vinylaromatic compounds having up to20 carbon atoms, ethylenically unsaturated nitrites, vinyl halides,vinyl ethers of alcohols containing 1 to 10 carbon atoms, aliphatichydrocarbons having 2 to 8 carbon atoms and 1 or 2 double bonds, ormixtures of these monomers.

Examples which may be mentioned are alkyl (meth)-acrylates containing aC₁-C₁₀-alkyl radical, such as methyl methacrylate, methyl acrylate,n-butyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate. Mixtures ofalkyl (meth)acrylates are also particularly suitable.

Vinyl esters of carboxylic acids having 1 to 20 carbon atoms are, forexample, vinyl laurate, vinyl stearate, vinyl propionate, vinyl estersof Versatic acid and vinyl acetate.

Suitable vinylaromatic compounds are vinyltoluene, α- andp-methylstyrene, α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene andpreferably styrene. Examples of nitriles are acrylonitrile andmethacrylonitrile.

The vinyl halides are chlorine-, fluorine- or bromine-substitutedethylenically unsaturated compounds, preferably vinyl chloride andvinylidene chloride.

Examples of vinyl ethers which may be mentioned are vinyl methyl etherand vinyl isobutyl ether. Preference is given to vinyl ethers ofalcohols containing 1 to 4 carbon atoms.

As hydrocarbons having 2 to 8 carbon atoms and 2 olefinic double bonds,mention may be made of butadiene, isoprene and chloroprene.

Besides these main monomers, further monomers, for examplehydroxyl-containing monomers, in particular C₁-C₁₀-hydroxyalkyl(meth)acrylates, (meth)acrylamide, ethylenically unsaturated acids, inparticular carboxylic acids, such as (meth)acrylic acid or itaconicacid, dicarboxylic acids and their anhydrides or monoesters, for examplemaleic acid, fumaric acid and maleic anhydride, can be used in thepolymer.

Conventional emulsion polymers generally comprise at least 40% byweight, preferably at least 60% by weight, particularly preferably atleast 80% by weight, of the above main monomers. Particularly preferredmain monomers are (meth)acrylates and vinylaromatic compounds, andmixtures thereof.

Aqueous polymer dispersions are generally used with solids contents offrom 15 to 75% by weight, preferably from 40 to 60% by weight. Thetypical particle size of the dispersed polymer particles is in the rangeof from 150 to 3000 nm, preferably from 150 to 900 nm. The viscosity istypically in the range from 15 to 500 mPa s, preferably from 15 to 200mPa s, at 23° C. in accordance with DIN EN ISO 3219 at a rate gradientof 100 l/s.

The application apparatus according to the invention as shown in FIG. 3an enabled uniform application of aqueous polymer dispersions at aweight per unit area of between 10 and 30 g/m² to be achieved onsiliconized paper or film at a surface speed of the engraved roll ofbetween 250 and 600 m/min. The resultant adhesive film on thesiliconized paper or on the film was of uniform, reproducible thicknessand was free from air inclusions. In particular, the film had excellenttransparency.

We claim:
 1. An apparatus for applying a flowable medium (2, 2′) to acontinuously transported web (1) which lies on a counterroll (5) in aregion where the medium (2, 2′) is applied, comprising the following: a)a continuously rotating engraved roll (4) adapted for applying medium(2, 2′) to web (1), b) the engraved roll (4) has on its circumferentialsurface (6) a plurality of engraved grooves (19), c) an application head(3) adapted for applying medium (2, 2′) to the circumferential surface(6) of the engraved roll (4), d) the application head (3) is arrangedbelow the engraved roll (4), and the engraved roll (4) is arranged belowthe counter roll (5), e) the application head (3) has a pre-chamber (7)and a main chamber (8), open toward the circumferential surface (6) ofthe engraved roll (4), for the medium (2, 2′) to be applied, f) thepre-chamber (7) and main chamber (8) are separated from one another by acenter sealing member (10), with the sealing member (10) lying on thecircumferential surface (6) of the engraved roll (4), g) the pre-chamber(7) is bounded on its exposed exterior side by a front doctor blade(13), which lies to form a seal on the circumferential surface (6) ofthe engraved roll (4) and the main chamber (8) is limited on its exposedexterior side by a back doctor blade (17) which also lies to form a sealon the circumferential surface (6) of the engraved roll (4), and h)pre-chamber (7) and main chamber (8) are adapted such that the pressureof the medium (2) in the pre-chamber (7) is greater than the pressure ofthe medium (2′) in the main chamber (8).
 2. Apparatus according to claim1, wherein the sealing member (10) arranged between pre-chamber (7) andmain chamber (8) is adjustable.
 3. Apparatus according to claim 1,wherein the sealing member (10) is a solid wiper (34).
 4. Apparatusaccording to claim 1, wherein the sealing member (10) has a flexibleplastic leaf (27) that is arranged such that at least one edge of theleaf (27) makes contact with the circumferential surface (6) of theengraved roll (4).
 5. Apparatus according to claim 1, wherein thepressure in the pre-chamber (7) is from about 300 mbar to 600 mbar, andthe pressure in the main chamber (8) is from about 100 mbar to 300 mbar.